Knowing how to write a pharmaceutical SOP (standard operating procedure) is one of the most underrated skills in GMP. A poorly written SOP generates deviations, operational errors and inspection findings; a clear, well-structured SOP is the first line of defence of the quality system. Yet most manufacturing sites do not have a truly applied internal standard for writing procedures.
This guide shows how to structure an SOP that meets the expectations of EudraLex Volume 4, Chapter 4 (Documentation), with a model structure, the operational steps from draft to approval and the mistakes most frequently challenged by inspectors.
What the regulations require
Chapter 4 of the EU GMP sets out the principles of good documentation: instructions must be approved, signed and dated by authorised persons, have unambiguous content, be uniquely identifiable and be kept current through revision control. In short, an SOP must be:
- Unique: title, identification code, version number and effective date.
- Clear: instructions written in the imperative, understandable by the operator who performs them.
- Controlled: defined review and approval workflow, managed distribution, withdrawal of obsolete versions.
- Verifiable: consistent with the records (forms, logs) that demonstrate its execution.
The model structure of a GMP SOP
There is no mandatory format, but consolidated industry practice includes recurring sections that cover regulatory expectations:
| Section | Content | Typical mistake |
|---|---|---|
| 1. Purpose | Why the procedure exists, in 2-3 sentences | Generic purpose that does not delimit the process |
| 2. Scope | Areas, departments, products and activities covered (and excluded) | Undeclared exclusions |
| 3. Responsibilities | Who performs, who verifies, who approves | Roles mentioned but inconsistent with the organisation chart |
| 4. Definitions and abbreviations | Technical terms and acronyms used in the text | Unexplained acronyms |
| 5. Procedure | Step-by-step instructions, in chronological order | Implicit steps “taken for granted” |
| 6. Documentation and records | Forms to complete, where and for how long they are archived | Forms referenced but not attached or not coded |
| 7. References | Standards, guidelines and related SOPs | References to obsolete documents |
| 8. Revision history | Version, date, description of the change | Generic descriptions such as “general update” |
How to write the SOP step by step
- Map the real process. Observe the activity on the floor and interview the people who perform it: the SOP must describe what actually happens, not an ideal process.
- Define the level of detail. Rule of thumb: a trained operator who is new to the department must be able to perform the activity without additional verbal instructions.
- Write in the imperative. Short sentences, one action per sentence, imperative verbs (“Verify”, “Record”, “Sign”). Avoid the passive voice and ambiguous cross-references.
- Build in the recording points. Every critical step must state what to record, where and who signs: this is what makes the procedure defensible in an audit.
- Have the draft reviewed by those who perform the activity. The best test is an operational walk-through: if the operator hesitates or improvises, the text needs fixing.
- Approve, train, make effective. QA approval, documented training of the personnel involved and only then the effective date, withdrawing the previous version.
The mistakes most challenged in inspections
- SOPs that are photocopies of guidelines, not adapted to the site's process.
- Divergence between the written procedure and the actual practice observed by the inspector.
- An excessive number of overlapping procedures that contradict each other.
- Undocumented training on the most recent revisions.
- Periodic review not performed: procedures formally in force but in fact obsolete.
GuideGxP recommendation
Before writing new procedures, define an “SOP on SOPs”: a master document that standardises format, coding, approval workflow, revision management and style rules for the whole site. It is the investment with the best effort/benefit ratio for documentation quality and drastically reduces writing time. A ready-made template already structured to GMP expectations also aligns the work of every author from day one.
